A data source is created, a folder that contains an Excel file. This data source was used by 6 users which crashes loading and access to the application. Is there a limitation on the number of users to use the same data source?

Can you elaborate exactly when u say 6 users , and what are you doing?

You should be able to use Quick Load and point to the file in the folder you want and it will load up a preview screen for you to select which sheets and columns to load into QlikSense. I do it a lot with no issues.